The present invention relates to a heterogeneous computer system comprising a host computer and a plurality of I/O subsystems, and more in particular to a method for making it possible to back up the data stored in a memory between a host computer and an I/O subsystem which cannot be directly connected due to the difference in access interface, and a heterogeneous computer system including a plurality of I/O subsystems having different access interfaces connected to the system and the host computer.
In mainframes, a large scale of memory hierarchy (storage hierarchy) including a combination of a plurality of external memories having different processing speeds and different storage capacities is accompanied by a satisfactory data management function and an overall storage management function intended to support an optimum data arrangement and an efficient operation. The IBM""s DFSMS (Data Facility Storage Management Subsystem) is an example, which is described in detail in xe2x80x9cIBM SYSTEMS JOURNAL, Vol. 28, No. 1, 1989, pp. 77-103.
The disk data of the I/O subsystem of the mainframe computer system having the above-mentioned management function can be backed up in a medium such as a magnetic tape or a magnetic tape library capable of storing a large quantity of data with a low cost per bit.
An open system such as a personal computer or a work station, unlike the mainframe, is not equipped with a magnetic tape or a magnetic tape library capable of storing a large quantity of data.
Generally, in an open system such as a personal computer or a work station, a disk is accessed in accordance with a fixed-length record format, while the mainframe accesses a disk in accordance with a variable-length record format called the count key data format.
As a result, the disk subsystem for the mainframe computer is often configured independently of the disk subsystem for the open system.
On the other hand, a technique for transmitting and receiving data between I/O subsystems is disclosed in U.S. Pat. No. 5,155,845.
In a disk subsystem for an open system and a disk subsystem for a mainframe computer which use different host computers, the back-up and other functions are independently operated and managed.
In view of the fact that the open system lacks a medium such as a magnetic tape or a magnetic tape library capable of storing a larger quantity of data, as described above, it is effective to back up the data in the I/O subsystem of the mainframe.
An ordinary disk system for the open system, however, cannot be connected directly to the mainframe due to the difference in the interface thereof.
U.S. Pat. No. 5,155,845 fails to disclose how to process the read/write operation for a storage system not directly connected to a host computer.
An object of the present invention is to provide a method and a system for backing up data stored in a memory between a host computer and an I/O subsystem that cannot be connected directly to each other due to the difference in access interface.
Specifically, an object of the invention is to provide a method and a system for backing up data stored in an I/O subsystem of an open system from a mainframe not directly connected to the I/O subsystem.
Another object of the invention is to provide a method and a computer system in which a mainframe is capable of accessing a memory of an I/O subsystem of an open system not directly connected to the mainframe.
Still another object of the invention is to provide a system and a method of access in which two or more I/O subsystems having different interfaces can be connected to a mainframe.
In order to achieve the above-mentioned objects, according to one aspect of the present invention, there is provided a heterogeneous computer system comprising a first host computer, a first I/O subsystem directly connected to the first host computer by an interface of variable-length record format and including at least one external memory, a second host computer, a second I/O subsystem directly connected to the second host computer by an interface of fixed-length record format and including at least one external memory, and a communication unit for connecting the first I/O subsystem to the second I/O subsystem;
wherein the first I/O subsystem includes a table for storing a device address of an external memory, data indicating one of the external memory of the first I/O subsystem and the external memory of the second I/O subsystem to which the device address is assigned, and a device address of the external memory in the second I/O subsystem when the device address is assigned to the external memory of the second I/O subsystem; and
wherein upon receipt of a read/write request conforming to the interface of variable-length record format from the first host computer and including an address of an external memory to be read from or written into, and upon decision, with reference to the table, that the external memory address included in the read/write request is assigned to the external memory included in the second I/O subsystem, the first I/O subsystem converts the read/write request into a second read/write request conforming to the interface of fixed-length record format and sends the second read/write request to the second I/O subsystem.
According to another aspect of the invention, there is provided a heterogeneous computer system comprising a first host computer, a first I/O subsystem directly connected to the first host computer by an interface of variable-length record format and including at least one external memory, a back-up system connected to the first host computer, a second host computer, a second I/O subsystem directly connected to the second host computer by an interface of fixed-length record format and including at least one external memory, and a communication unit for connecting the first I/O subsystem to the second I/O subsystem;
wherein the first host computer includes a means for issuing to the first I/O subsystem a read request conforming to the interface of variable-length record format and containing the address of an external memory from which data is to be read, and backing up the data received from the first I/o subsystem into the back-up system;
wherein the first I/O subsystem includes a table for storing the device address of an external memory, data indicating that one of the external memory of the first and the second I/O subsystems to which the device address is assigned, and the device address of the external memory in the second I/O subsystem when the first device address is assigned to the external memory of the second I/o subsystem; and
wherein upon receipt from the first host computer of a read request conforming to the interface of variable-length record format including an external memory address to be read, and upon decision, with reference to the above-mentioned table, that the device address of the memory address included in the read request is assigned to the external memory included in the second I/O subsystem, the first I/O subsystem converts the read request into a second read request conforming to the fixed-length interface and sends the second read request to the second I/O subsystem while at the same time sending to the first host computer the data received from the second I/O subsystem.
According to still another aspect of the invention, there is provided a heterogeneous computer system comprising a first host computer, a first I/O subsystem directly connected to the first host computer by an interface of variable-length record format and including at least one external memory, a back-up system connected to the first host computer, a second host computer, a second I/O subsystem directly connected to the second host computer by an interface of fixed-length record format and including at least one external memory, and a communication unit for connecting the first I/O subsystem to the second I/O subsystem;
wherein the first host computer includes a means for issuing to the first I/O subsystem a write request conforming to the interface of variable-length record format including the address of an external memory into which data is to be written, and sending the data read from the back-up system to the first I/O subsystem;
wherein the first I/O subsystem includes a table for storing the device address of an external memory, data indicating that one of the external memory of the first and the second I/O subsystems to which the device address is assigned, and the device address of the external memory in the second I/O subsystem when the first device address is assigned to the external memory of the second I/O subsystem; and
wherein upon receipt from the first host computer of a read request conforming to the interface of variable-length record format including the device address an external memory to be written into, and upon decision, with reference to the table, that the address of the external memory included in the write request is assigned to the external memory included in the second I/O subsystem, the first I/O subsystem converts the write request into a second write request conforming to the interface of fixed-length record format, sends the second read request to the second I/O subsystem while at the same time sending the data received from the first host computer to the second I/O subsystem.
According to yet another aspect of the invention, there is provided a heterogeneous I/O system for use with a host, computer connected thereto, comprising a first I/O subsystem including at least one external memory, and a second I/O subsystem connected to the first I/O subsystem and including at least one external memory;
wherein the first I/O subsystem includes a table for storing a device address of an external memory, data indicating one of the external memories of the first and the second I/O subsystems to which the device address is assigned, and a device address of the external memory in the second I/O subsystem when the first device address is assigned to the external memory of the second I/O subsystem;
wherein upon receipt of a read/write request designating the device address of an external memory to be read from or written into by the host computer, and upon decision, with reference to the table, that the external memory address in the designated address is assigned to the external memory included in the second I/O subsystem, the first I/O subsystem sends the read/write request to the second I/O subsystem.
According to a further aspect of the invention, there is provided a heterogeneous I/O system for use with a host computer connected thereto, comprising a first I/O subsystem having an interface of variable-length record format and including at least one external memory, a second I/O subsystem having an interface of fixed-length record format and including at least one external memory, and a communication unit for connecting the first I/O subsystem to the second I/O subsystem;
wherein the first I/O subsystem includes a table for storing a device address of an external memory, data indicating one of the external memories of the first and the second I/O subsystems to which the device address is assigned, and a device address of the external memory in the second I/O subsystem when the first device address is assigned to the external memory of the second I/O subsystem; and
wherein upon receipt from the host computer of a read/write request conforming to the interface of variable-length record format including the address of an external memory to be read from or written into, and upon decision, with reference to the table, that the external memory address included in the read/write request is assigned to the external memory included in the second I/O subsystem, the first I/O subsystem converts the read/write request into a second read/write request conforming to the interface of fixed-length record format and sends it to the second I/O subsystem.
According to an embodiment of the invention, there is provided a heterogeneous computer system, wherein an I/O subsystem for an open system is connected to an I/O subsystem for a mainframe by a communication unit, wherein, in order to access data in the I/O subsystem for an open system from the mainframe for enabling the data in the disk connected to the I/O subsystem for the open system to be backed up in a magnetic tape library system; a table is prepared for assigning a vacant address of the memory in the local subsystem to the memory of the I/O subsystem for the open system, wherein a request of variable-length record format received from the mainframe is converted into a request of fixed-length record format for the open system; wherein the disk designated according to the table is accessed, and wherein the data thus obtained is sent to the mainframe and backed up in the back-up system.
This configuration can back up the data of an I/O subsystem for an open system in a back-up system under the management of a mainframe not directly connected to the particular I/O subsystem.